Two modes are supported in 3GPP E-UTRA (Third Generation Partnership Project-Evolved Universal Terrestrial Radio Access) systems: frequency division duplexing (FDD) mode and time division duplexing (TDD) mode. For the TDD mode, the duration (length) of a radio frame is 10 milliseconds (ms) and the radio frame includes two 5 ms length half-frames. Each half-frame includes eight 0.5 ms timeslots and three special fields. Two timeslots form a subframe, and the three special fields together form a special subframe. The three special fields are a downlink pilot timeslot (DwPTS), a guard period (GP) and an uplink pilot timeslot (UpPTS). The length of each subframe is 1 ms.
Currently, in the 3GPP E-UTRA systems, there are two modes for feeding back, in an uplink subframe, acknowledgement or negative acknowledgement (ACK/NAK) information of multiple downlink subframes. The two modes are multiplexing mode and bundling mode. In the multiplexing mode, if a feedback is carried in a physical uplink control channel (PUCCH), the feedback is related to an uplink-downlink configuration. If the feedback is carried in a physical downlink shared channel (PDSCH), the number of feedback bits depends on whether there is an uplink grant (UL Grant) signaling. If there is the UL Grant signaling, the number of bits that a user equipment device (UE) is required to feed back is specified through an uplink data assignment indicator (UL DAI) field of the UL Grant signaling. For example, if a base station (BS) schedules a number x of the total N downlink subframes, the UE feeds back x ACKs/NAKs. If there is no UL Grant signaling, the UE feeds back N bits of ACK/NAK, and a non-scheduled downlink subframe corresponds to a NAK.
In the bundling mode, no matter whether the feedback information is carried in the PUCCH or in the PUSCH, only 1-bit ACK/NAK information is sent to represent all the scheduled downlink subframes. As long as the feedback to one of the scheduled downlink subframes is a NAK, the feedback sent is a NAK. Only when feedbacks to all the scheduled downlink subframes are ACKs, the feedback sent is an ACK.
Two scheduling modes are defined in the current Long Term Evolution (LTE) protocol: dynamic scheduling mode and semi-persistent scheduling (SPS) mode. This means there are two ways of indicating resources for data transmission. In the dynamic scheduling mode, for each new data packet, there is a control signaling in a physical downlink control channel (PDCCH) to indicate a resource and a transmission mode. The UE receives downlink data and transmits uplink data according to the PDCCH sent by the base station (BS). In the SPS mode, the BS sends a PDCCH control signaling only when the SPS transmission is activated. The UE activates the SPS transmission according to the position and time indicated by the PDCCH. The UE transmits and receives data packets periodically, until another PDCCH in a special format is received, which terminates the SPS transmission.
Because the PDCCH is used for indicating both dynamic scheduling mode and semi-persistent scheduling mode, the UE differentiates whether the scheduling mode is the dynamic scheduling or the semi-persistent scheduling by recognizing different identifiers (IDs) used in scrambling a cyclic redundancy check (CRC) of the PDCCH. In the dynamic scheduling mode, the CRC of the PDCCH is scrambled with a cell radio network temporary identifier (C-RNTI). In the semi-persistent scheduling mode, the CRC of the PDCCH is scrambled with a semi-persistent scheduling cell radio network temporary identifier (SPS-C-RNTI). When the UE detects that the PDCCH is scrambled with the SPS-C-RNTI, the UE activates the semi-persistent transmission, and receives or transmits data according to the indication in the PDCCH. Within a subsequent period of time, the UE receives and transmits data only according to the position indicated by the PDCCH when the semi-persistent transmission is activated, making it unnecessary to notify the UE each time of the positions of resources for SPS data packets through the PDCCH. When the positions of the SPS resources need to be changed, a new PDCCH may be used to replace the previous semi-persistent scheduling configuration at the end of the period of the SPS data transmission. The semi-persistent transmission is cancelled by a PDCCH scrambled with an SPS-C-RNTI in a special format.
In the uplink ACK/NAK multiplexing mode of the prior art, the first position of K ACKs/NAKs fed back by the UE is the ACK/NAK of a SPS subframe, and the positions of the ACKs/NAKs of other subframes are arranged in the sequence of downlink data assignment indicator (DL DAI). If the UE does not detect data in a subframe, the UE feeds back a NAK. If the UE did not receive the SPS activation signaling, the UE feeds back a NAK at the first position. Based on the NAK, the BS thinks that the control signaling is received properly but data is wrong, thus the feedback information is incorrectly received. As a result, the BS does not retransmit a PDCCH, and the UE still does not know the position of the semi-persistent transmission, which causes unnecessary retransmission.